1. Field of the Invention
The present invention relates to a freeze forecasting device for a hot water heating apparatus, for forecasting freeze of water in a water passage circuit. More specifically, the present invention relates to the freeze forecasting device for forecasting a possibility of freeze of water in a water passage circuit of a hot water heating apparatus such as a bath reheating apparatus, a water heater, a hot water heating system, and the like.
2. Description of the Related Art
As a bath reheating apparatus, there is a widely known reheating apparatus in which a heat exchanger heated by a gas burner and a bathtub are connected by a reheating circuit in a closed loop form and a forced-circulation pump is disposed in the reheating circuit. Moreover, as this type of reheating apparatus, there is a known reheating apparatus mounted with an outside air temperature sensor for preventing freeze, because there is a fear that water in the reheating circuit freezes as outside air temperature drops during shutdown in winter.
In this reheating apparatus, if the gas burner is turned on to actuate the forced-circulation pump, bath water in the bathtub is heated by the heat exchanger while circulating through the reheating circuit in the closed loop form to be thereby reheated.
Furthermore, there is a known reheating apparatus in which when an outside air temperature sensor detects that an outside air temperature has dropped to a freezing critical temperature in a state in which a bathtub is filled with water, a forced-circulation pump is operated intermittently to thereby prevent freeze of water in a reheating circuit in winter.
However, in each of the above-described conventional reheating apparatuses, because the forced-circulation pump is suddenly actuated to start the freeze preventing operation when the outside air temperature drops at cold midnight in winter, noise of the pump suddenly echoes in a room where a resident is fast asleep to thereby disturb him/her.
Although a problem of the bath reheating apparatus has been taken as an example, a circulation pump is also actuated during a freeze preventing operation in a hot water heating apparatus such as a hot water heating system in which hot water produced by heating by a heat exchanger is supplied to heating terminal equipment with the circulation pump. Therefore, this kind of hot water heating apparatus such as the hot water heating system also has the problem similar to the above.